Oxidation of aromatic compounds



Patented Nov. 21, 1950 UNITED STATES PATENT OFFICE OXIDATION OF AROMATIC COMPOUNDS Joseph H. Simons, State College, Pa., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application January 29, 1948, Serial No. 5,205

20 Claims. 1

containing products other than phenolic contain the same carbon ring structure as the reactant.

In the past, several processes have been proposed for production of aromatic ring substituted hydroxy (phenolic) compounds by partial oxidation of aromatic hydrocarbons. Such processes employ a wide variety of methods in which the oxidations are conducted principally in the gaseous phase, with and without catalysts or contact surfaces. In all such processes, high temperatures must be employed 1. e., tempera tures greatly in excess of 200 C., as evidenced by the following United States patents: Bibb No. 1,547,725 (700 C.), Hale No. 1,595,299 (greater than 300 C.). Bone et al. No. 2,199,585 (200400 C.), Moyer et al. Nos. 2,223,393 (325-800 C.) and 2,328,920 (650 0.). Furthermore, these processes result in the formation of undesired by-products such as those produced by ring rupture, side chain oxidations and relatively complete combustion, for example, allphatic acids, aromatic aldehydes, and particularly gases such as carbon dioxide, carbon monoxide. Inflammable gaseous hydrocarbons and tars are often formed as a result of cracking at the high temperatures employed.

All such prior art processes are limited in their application to the use of either benzene or benzene and toluene as reactants. In addition, with a single exception (Moyer et al. Nos. 2,223,393

and 2,328,920), all of the processes as applied to toluene result in oxidation of the alkyl side chain to produce benzyl alcohol, benzaldehyde and benzoic acid (see Bone et al. 2,199,585) rather than formation of cresols.

Of course, there are many existing processes wherein higher homologues of benzene and the like are oxidized to produce products typical of side chain oxidation, such as benzyl alcohol, aldehydes, and mono and dicarboxylic acids. However, such oxidations occur much more readily than those involving introduction of an oxy group into the nucleus of an aromatic hydrocarbon. This invention is concerned primarily with the latter type of oxidation.

According to the present invention, it has been discovered that aromatic hydrocarbons are oxidized to predominantly phenolic products in high yield in the presence of liquid hydrogen fluoride, and that the carbon-containing byproducts, if any are formed, contain the same carbon ring structure of the reactant with little or no oxidation of side chains if such are present.

Essentially, the process of the present invention comprises oxidizing an aromatic hydrocarbon with an oxidizing agent at temperatures ranging from 0 C. to 200 C. in the presence of liquid hydrogen fluoride.

Very high yields of phenolic compounds are obtained to the exclusion of products typical of side chain oxidations which are formed in negligible amount when such hydrocarbons as toluene, xylene, methyl naphthalene and the like are utilized as reactants. Furthermore, the formation of typical ring rupture products, such as allphatic compounds, and gaseous products of relatively complete combustion, i. e., carbon dioxide and carbon monoxide are not produced in substantially all instances.

One of the principal advantages of the present invention resides in the use of liquid hydrogen fluoride in the reaction medium which causes ring oxidation to occur in preference to side chain oxidation.

It is believed that the oxidation reaction proceeds as follows: Hydrogen fluoride activates the hydrogen on the ring of the aromatic compound more than on a side chain. The strong dehydrating action of the hydrogen fluoride tends to favor the oxidation. This oxidation in the presence of hydrogen fluoride seems also to be imusual in that the oxides of carbon and products which would normally result from the breaking of the aromatic ring are not produced.

Another distinct advantage flowing from the use of liquid hydrogen fluoride is that the reaction will proceed effectively and result in theoretical and near theoretical yields of phenolic products even at comparatively low temperatures within the range above set forth. This eliminates the formation of tars and inflammable lower aliphatic hydrocarbon gases commonly produced by cracking and ring rupture in the prior art processes where much higher temperatures are employed. In fact, the process of the present invention cannot be operated at temperatures above 230 C. regardless of the pressure of the system since this temperature i the critical temperature of hydrogen fluoride and the reaction involves the use of hydrogen fluoride in the liquid phase.

A further unexpected result characterizing the process of this invention is that the so-called complete combustion products or more properly the end products are a valuable activated carbon containing the ring structure of the aromatic hydrocarbon reactant and water. Thus, if the reaction is carried out at temperatures approaching the maximum for the process, and the reaction time is prolonged, the hydrocarbon will eventually be oxidized completely to such activated carbon and water. The formation of such a product as activated carbon in such an oxidation process is'unusunl and striking.

It has further been found that the only products resulting from the process as applied to non-aromatic compounds are activated carbon and -water. This novel method of producing activated carbon from non-aromatic compounds is disclosed and claimed in my copending application Serial No. 424,214, filed December 23, 1941,

now U. S. Patent 2,458,107, issued January 4, 1949. The carbon formed is an absorbing or activated char which does not require further processing for activation. As a rule such activated chars cannot be prepared by oxidation of hydrocarbons, but result from dehydration of carbohydrates.

In addition to the phenolic compounds, other products which are in some instances formed in the process of the invention include plural ring systems, such as diphenyl, ditolyl, di and tri naphthyls, di and tri xylyls.

The formation of benzoic acid in the process in some cases where benzene is employed appears to be extremely noteworthy. It is believed that this aromatic monocarboxylic acid has never before been synthesized by oxidation of benzene. This formation of benzoic acid was the only instance in which compounds other than those having the same carbon ring structure as the initial reactants are formed. It is thought that the hydrogen fluoride activates the hydrogen atoms on the benzene ring to the point of removal, which results in the formation of diphenyl between two adjacent benzene molecules. One ring of the diphenyl thus formed is ruptured leading to the formation of benzoic acid. The by-products occurring with benzoic acid were not identified except that in every case where it formed, diphenyl was found to be present. However, it is not intended to limit the invention to the foregoing mechanism or any other theory of action, it being sufficient to state that in some instances where the yield of phenolic compounds is not 100%, benzoic acid is formed from benzene.

It is a further distinct characteristic of the present invention that it is in no way limited to the oxidation of benzene to produce phenol, but is applicable to aromatic hydrocarbons generally including such compounds as benzene, naphthalene, anthracene, phenanthrene and homologues or alkylated derivatives such as toluene, xylene, methylnaphthalene and the like.

Oxygen and oxygen-containing gases, such as air, as well as solid or liquid oxidizing agents may be employed in the process for efiecting the oxidation of the aromatic compound. However, air or gaseous oxygen are the preferred oxidizing agents from practical and economical considerations.

It has been found desirable but not essential to the practice of this invention to employ an "oxygen carrier. The term oxygen carrier as contemplated by the invention is used in its accepted sense, namely, an element or compound of an element which in a reaction medium where both oxidizing and reducing conditions simultaneously exist will reversibly change its valence. Thus, the particular substance acts as a means of transporting the oxygen from the available source, that is, the oxidizing agent to the reducing substance, that is, the aromatic hydrocarbon to be oxidized. A great variety of substances have been found suitable for this purpose. These include finely divided silver, silver oxide, silver fluoride, etc. the element or oxides of arsenic, selenium, iron, molybdenum, vanadium,

uranium, tungsten, manganese, chromium, copper, etc.; seienicacid, arsenic acid, etc. Although the carrier is frequently added as the element or oxide, the fluorides or oxyfluorides are certainly present in most cases due to the action of the anhydrous hydrogen fluoride. Because of the oxidizing action of the oxygen or other oxidizing agent present and also due to the reducing action of the organic substance, the valence of the oxygen carrier is afforded an opportunity to reversibly change.

It thus makes little difference in what chemical form the oxygen carrier is used. For example, the silver may be added either as the metal, the oxide, the-fluoride, the bromide, etc., while the arsenic may be added as arsenious acid, arsenic acid, or the salts of either of these acids, arsenious oxide, arsenic oxide, arsenic trlchloride, arsenic pentachloride, arsenic trifiuoride, arsenic pentafluorlde, or as any of the oxychlorides, bromides, fluorides, etc.

Although the addition of an oxygen carrier is preferred it is not essential for carrying out the oxidation process since the oxidation reaction will take place in the absence of any added oxygen carrier. Because of the extremely wide range of substances that may be used as oxygen carriers, it is believed, as above stated, that these substances act as a means of transporting the oxidation properties of the oxygen source to the molecules of the aromatic compound to be oxidized and, therefore, that any substance which can reversibly undergo a valence change in the same reaction medium can serve in this capacity. For example, silver can both dissolve the oxygen and carry it in the dissolved condition to the aromatic compound, or it can form silver oxide, fluoride or oxyfiuoride with the attendant valence change and thus carry the oxidizing property. The arsenic compounds, for example, can undergo the valence change from the three to the five valent forms and vice versa, thus serving as the oxygen carriers.

In some cases mixtures of oxygen carriers may be employed in carrying out the oxidation-reduction reaction. Without the addition of the carrier to the reaction mixture, the reaction rate is slower. All the oxygen carriers act in a similar manner, but there are some minor differences. Arsenic and selenium compounds cause the reaction to take place at relatively low temperatures, while molybdenum oxide causes larger amounts of activated carbon, dimers, and carboxylic acids to be formed at the expense of the yield of phenolic compounds.

The reaction takes place either homogeneously in the liquid phase or heterogeneously between the liquid and solid phases. In the homogeneous liquid phase oxygen carriers which are soluble in this phase aid in increasing the rate of the reaction. For the heterogeneous case the larger the amount of solid surface the faster the rate. A large amount of finely divided solid substance, such as copper, nickel, iron, silver, Monel, carbon, etc., is beneficial. When oxygen, air or other oxygen-containing gas is used as the oxidizing agent, the rate of the reaction to a large extent is governed by the rate of solution of oxygen or gas into the liquid phase and this depends upon the amount of surface between gaseous and liquid phases. Introducing the gas into the liquid in the form of small bubbles is beneficial as is also vigorous agitation of the mixture. Another way of providing a large amount 01' surface is to flow the liquid as a film over solid packing in a reaction tower where a large amount of surface is provided exposed to the surrounding gas. Carbon packing is preferred, although any of the abovementioned finely divided solids may be used.

The process may be operated either as a batch process or in a cyclic manner. The latter is highly preferred insofar as conversions per pass are often quite small. An exemplary method embodying the cyclic process is conducted as follows: A reaction tower consisting of a metallic tube or pipe is packed with a finely divided solid oxygen carrier and provided with external heating means for obtaining the desired reaction temperature. The tower is then filled with liquid hydrogen fluoride. The aromatic hydrocarbon such as benzene is fed into the reaction column at the bottom thereof at the desired controlled rate. Atmospheric air is also fed into the column at the bottom at the desired rate and pressure. Excess air is exhausted at the top of the tower, which is provided with a condenser so as to return liquid substances to the reaction zone. Unreacted aromatic hydrocarbon, phenolic and other reaction products and hydrogen fluoride are discharged from the top of the tower into a stripping still. The overhead of the stripping still containing unreacted hydrocarbon and hydrogen fluoride is returned to the feedline of the reaction tower, and the bottoms of the still constitute the recovered crude phenolic products, and other products, if formed. In many instances the yield of phenolic compound based on the amount of hydrocarbon consumed either equaled or approached 100%, that is, the conversion efiiciency was extremely high, but the action tower packed with a finely divided subconversion per pass based on total hydrocarbon present was low. However, by merely recycling with removal of product formed in each pass near theoretical yields are obtained.

An exemplary method for practicing the invention as a batch process comprises placing the aromatic compound in a metal reaction chamber, such as an autoclave, with liquid hydrogen fluoride and an oxygen carrier. To the reaction chamber is attached a reflux condenser, the apparatus being equipped with appropriate valves and gauges. The reaction chamber is preferably placed in a heater on a shaking machine or other suitable device for effecting agitation. When a solid or liquid oxidizing agent is employed, it may be added before connecting the reflux condenser. If a gaseous oxidizing agent such as air, oxygen, or other oxygen-containing gas is employed, such gaseous oxidizing agent may be directly admitted under the desired pressure to the reaction charmber which is heated to the desired temperature. After the reaction is completed, the excess gases may be exhausted from above the reflux condenser. The hydrogen fluoride and the reaction products are thus retained in the vessel. The reaction products may be separated by distillation, crystallization, or other commonly used method. The hydrogen fluoride employed to effect the reaction may be purified by distillation and thus made available for reuse.

As stated above, when a gaseous oxidizing agent such as air or molecular oxygen, is employed the reaction rate to a large extent is governed by the rate of solution of oxygen or gas into the liquid phase. This depends not only on the amount of surface between the gaseous and liquid phases, but also to some extent on the pressure in'the system. When the process is conducted in an autoclave or in a packed pressure column, as above described, the pressure can be varied over stance which may or may not act as an oxygen carrier, for example, iron, copper, nickel, silver, Monel metal or carbon. A mixture of aromatic hydrocarbon and liquid hydrogen fluoride is fed to the top of the tower from which it flows slowly downward while air or oxygen introduced at the bottom of the tower flows upward countercurrently. A liquid take-off provided at the bottom of the tower is connected to a stripping column for separating the reaction mixture. The overhead of the stripping column containing unreacted hydrocarbon and hydrogen fluoride is returned to the tower feed line and the bottoms in the stripping column constitute the crude phenolic products. When oxygen rather than air is used, no exhaust need be provided for gas at the top of the column provided that the oxygen feed rate is adjusted to only make up for that used. Furthermore, no gaseous products are formed. The temerature-pressure conditions are maintained to insure against vaporization of the hydrogen fluoride and hydrocarbon.

This method of practicing the invention advantageously presents an extremely large contact surface between the gaseous and liquid reactants. Thus, the extremely thin films of liquid flowing through the interstices of the solid packing are brought into intimate contact with the surrounding gas. In this procedure, the amount of surface provided causes a satisfactory rate of reaction at pressures much lower than the superatmospheric range above stated. In fact, even at the lower temperatures, a pressure of the order of atmospheric will give a satisfactory rate of reaction.

The molecular ratio of hydrocarbon to hydrogen fluoride may be varied within extremely wide limits without affecting the mechanism of the reaction to form the desired product. In some instances when the ratio exceeds 3 to 1 undesirable oxidation begins to occur, such as formation of the oxides of carbon. On the other hand, however, ratios as low as 1 to 333 produce a conversion efliciency of A mole ratio of 1 to 2 has also been found to be extremely satisfactory, and therefore the preferred range is any ratio of 3 to 1 or less.

The oxidation process can be carried out at temperatures as low as 0 C., but at such temperature the reaction rate is slow. Room temperatures can be effectively employed particularly when using a very large amount of contact .surface, such as embodied in the third alternative procedure utilizing a packed column.

The process is governed by a series of rate phenomena not equilibria. Several reactions are involved in the process, the first few of which produce the only oxy en-containing products, namely, the phenolic compounds and the carboxylic compounds such as benzoic acid. Generally, if a completely condensed ring product (activated carbon) is desired high temperatures and longer reaction times employed. The optimum range for high conversion efllciencies for phenolic products is between 50 C. and 125 C. and this range is therefore preferred. However, lower temperatures may be employed although the reaction rate is slower, and temperatures as high as 200 C. may also be employed, although carbon formation becomes more pronounced at the higher temperatures.

It is to be not d that when certain diluents, such as water, methanol and ethanol are employed,

the formation of benzoic acid, and dimers and trimers of the aromatic hydrocarbon is favored. These diluents also tend to necessitate higher reaction temperatures. Increased formation of these products was also found to occur when molybdenum compounds were used as the oxygen carrier.

Generally, when employing a gaseous oxidizing agent such as air or molecular oxygen in the autoclave or packed tube embodiments, that is, the flrst two of the above-described alternative procedures, it is preferred to operate at pressures between 500 and 1000 pounds per square inch, at temperatures between 50 C. and 120 C. It is to be understood that these conditions may be varied. In particular, the pressure employed may be of the order of atmospheric when utilizing a large amount of contact surface.

The following examples are illustrative of the process. In the examples the parts referred to are parts by weight, the temperatures are given in degrees centigrade, and the pressure is given in pounds per square inch.

Example 1 To 234 parts of benzene were added 120 parts of hydrogen fluoride and 30 parts of silver oxide. The mole ratio of benzene to hydrogen fluoride was 1:2. 900 pounds per square inch gauge pressure of oxygen were added. The furnace was heated to 65 C. for two hours with shaking. No carbon monoxide, carbon dioxide, or inflammable gases were found in the products. No carbon was formed. Phenol was the only solid or liquid organic product other than benzene that was found in the products. Thus, the 1.3 parts of phenol obtained represented approximately a 100 percent yield based on the amount of benzene consumed, that is, 100% conversion efficiency.

Example 2 To 234 parts of benzene were added 75 parts of hydrogen fluoride and 30 parts of arsenious oxide. Oxygen was added at 1000 pounds gauge pressure, and the reaction vessel was shaken and heated to 80 C. for three and one-half hours. No carbon monoxide, carbon dioxide, or inflammable gases were found in the products. No carbon was produced. 1.1 parts of phenol were obtained, and no other organic substance except benzene was found. This represents a 100% conversion efliciency.

Example 3 To 135 parts of benzene were added 70 parts of hydrogen fluoride and 8 parts of selenium oxide. Oxygen at 1000 pounds per square inch pressure was added, and the vessel was heated to 100 C. for three hours. 1.3 parts of phenol were obtained, and there were no detectable amounts of carbon monoxide, carbon dioxide, or inflammable gases. The phenol obtained represented a 77 percent conversion efllciency or yield based on the amount of benzene consumed. The remainder of the benzene consumed was converted to a flue soft carbon.

Example 4 These products represented yields of 6 percent and 84 Percent, respectively, based upon the amount of toluene consumed. This demonstrates that nuclear oxidation occurs in preference to side chain oxidation in the presence of liquid hydrogen fluoride. The remainder of the toluene consumed formed an activated carbon.

Example 5 To 318 parts of meta-xylene were added 126 parts of hydrogen fluoride and 32 parts of silver oxide. Oxygen was added at 1050 pounds per square inch. The vessel was shaken at 120 C. for six hours. No carbon monoxide, carbon dioxide, or inflammable gases were found. 0.1 part of carbon was produced. 0.2 part of metatoluic acid and 0.! part of 2,4-dimethyl phenol were obtained. This represents a conversion efliciency of 70% based on m-xylene consumed for production of 2.4-dimethylphenol.

Example 6 To 115 parts of naphthalene were added 139 parts of hydrogen fluoride and 34 parts of iron oxide. The oxygen was added at 1000 pounds per square inch, and the vessel was heated to 140 C. with shaking for three hours. 0.3 part of beta naphthol was obtained.

Example 7 A reaction tower was provided consisting of an iron pipe packed with ferric oxide and held in a vertical position. It was provided with external electrical heating and maintained at a temperature of 50. It was initially filled with liquid hydrogen fluoride. Benzene was fed at the bottom of the column at the rate of 0.90 liter per hour. Atmospheric air at the rate of cc. per second (calculated at standard temperature and pressure) was also fed at the bottom at a pressure, of 500 pounds per square inch. The excess air was exhausted at the top of the tower through a condenser so as to return liquid substances. Liquid benzene, phenol and hydrogen fluoride flowed from the top of the tower into a stripping still. The overhead of the stripping still was returned to the feed line of the tower and the bottoms of the still were crude phenol. No carbon was produced. About yield and 1% conversion to phenol resulted.

Example 8 In this example the process of Example 7 was varied by using oxygen gas instead of air and a tower temperature of 70. The benzene feed rate was increased to two liters per hour and a faster rate of production of phenol resulted gith approximately the same yield and conver- Q The following examples are further illustrative of the process of the present invention:

remainder of the benzene consumed was converted to a soft finely divided carbon. indicating Per Cent Per Cent Per Cent Initial Final Yield B 1' Time Phenol Carbon Example No. figfig Oxygen Carrier Oxygen Texan, Hour; W on based on Pgergig l i aggd Benzene Benzene Used 1 F010; 786 03 4. 2. l5 0. 0 100 11100 do 765 lfl 0. 0 l. 0.0 100 1130 m0; 825 1m 7. 5 2. 73 16. 5 U2 C110 5m 85 2. 0 0. 790 0. 0 100 l/2 5.4g, lCu. 525 70 6. 0 0. 69 0.0 100 l/2 5.4g, ICu, 11110 400 65 3.0 1.000 0. 0 100 In Example 11, 85% of the phenol was converted to carbon which indicates that carbon formation is more pronounced with temperatures approaching the maximum and when the reaction time is prolonged.

Example 15 To '18 parts of benzene were added 120 parts of liquid hydrogen fluoride. This is a mole ratio of 1:6. No oxygen carrier was added. Oxygen at 50 pounds per square inch pressure was added and the temperature raised to 150 C. with agitation for seven hours. The reaction vessel was then cooled and its contents examined. No carbon monoxide, carbon dioxide, or any inflammable gas was found. One-fifth of a part of phenol was obtained, which represented a yield of 28 percent based on the amount of benzene consumed. The remainder of the benzene consumed was converted to carbon. This run again indicates carbon formation is favored at the higher temperatures and prolonged reaction time.

Example 16 To 234 parts of benzene were added 160 parts of hydrogen fluoride and 30 parts of silver oxide. The mole ratio of hydrocarbon to hydrogen fluoride was 1:26. Oxygen was added at 700 pounds per square inch and held at this pressure for two hours with shaking at room temperature (25 C.). No carbon monoxide, carbon dioxide, or inflammable gases were detected after reaction. A small amount of phenol was obtained.

Example 17 To 234 parts of benzene were added 120 parts of hydrogen fluoride and 200 parts of silver oxide. This mixture was heated for four hours at 80 C. with agitation. In the products were found 1.5 parts of phenol, which represented the only organic substance other than benzene. Carboncontaining gases were not found.

Example 18 To 234 parts of benzene were added 120 parts of hydrogen fluoride and 35 parts of flnely divided silver. Oxygen at 1000 pounds gauge pressure was added and the reaction vessel heated to 85 C. for three hours with shaking. From the reaction mixture 1.2 parts of phenol were obtained and no other organic substance was present except unreacted benzene.

Ex mple 19 To 284 parts of benzene were added 120 parts of hydrogen fluoride and 32 parts of molybdenum oxide. Oxygen was added at 1000 pounds per square inch pressure, and the vessel was heated at 100 C. with shaking for three and one-half hours. No carbon monoxide, carbon dioxide, or inflammable gases were found. 0.8 of a part of biphenyl and also 0.3 of a part of benzoic acid were obtained. These represented 10 per cent and 5 per cent yields, respectively,

Example 20 To 234 parts of benzene were added 128 parts of hydrogen fluoride, 30 parts of arsenic oxide, and 18. parts of water. Oxygen was added at 1000 pounds per square inch, and for four hours the vessel was shaken at C. No carbon monoxide, carbon dioxide, or inflammable gases were obtained. 0.1 of a part of phenol and 0.2 of a part of biphenyl were obtained, representing 21% phenol and 25% biphenyl based on the benzene consumed.

Example 21 To 234 parts of benzene were added 135 parts of hydrogen fluoride, 30 parts of arsenic oxide, and 84 parts of methanol. Oxygen was admitted at 1000 pounds per square inch pressure. The vessel was shaken for seven hours at C. No

carbon monoxide, carbon dioxide, or inflammable gases were obtained. 0.2 of a part of phenol and 0.1 of a part of biphenyl were obtained. A conversion efflciency of 51% as to phenol and 16% as to biphenyl is represented by these results.

Example 22 To 234 parts of benzene were added 128 parts of hydrogen fluoride, 30 parts of arsenic trioxide and 36 parts of water. Oxygen was added at 1400 pounds per square inch and for eight hours the vessel was shaken at 200 C. No carbon oxides or inflammable gases were obtained. A conversion efllciency of 6% phenol, 17% benzoic acid, and 4% biphenyl was obtained, the remainder of benzene consumed forming carbon.

Examples 20 to 22, inclusive, indicate the effect of water and methanol as diluents which favor formation of benzoic acid and biphenyl. The 200 C. temperature of Example 22 definitely favored carbon formation although 6% phenol was formed.

Example 23 To 234 parts of benzene were added 120 parts of hydrogen fluoride. No additional oxygen carrier was added. Oxygen was added at 850 pounds per square inch pressure. The vessel was heated to 130 C. with shaking for one hour. 2.7 parts of benzoic acid and 0.8 part of phenol were obbased on the amount of benzene consumed. The 75 tained.

Example 24 156 parts of benzene and 300 parts of hydrogen fluoride were placed in a copper vessel equipped with a reflux condenser. With the vessel at room temperature, oxygen was bubbled throu h the liquid mixture at atmospheric pressure at a rate of 12 liters per hour for live hours. A trace of phenol was obtained.

The foregoing examples are illustrative of the broad application of the invention to the preparation of aromatic hydroxy and aromatic carboxy compounds and other oxidation products containing the same carbon ring structure as the reactant which do not contain oxygen, such as condensed ring derivatives and activated carbon by oxidation in the presence of liquid hydrogen fluoride. It is to be understood that the specific reaction conditions will vary, depending upon the particular material being oxidized and the product desired.

The present application is in part a continuation of my copending application No. 424,215, filed December 23, 1941, and now abandoned.

The foregoing description is given by way 01' exemplifioation of the invention and is not to be construed in limitation thereof. the invention being limited only by the scope of the subjoined claims.

Having thus described my invention, I claim:

1. A process of ox dizing aromatic hydrocarbons selected from the group consisting of benzene, naphthalene, anthracene, phenanthrene, and homologues thereof to produce phenolic compounds which comprises oxidizing an aromatic hydrocarbon selected from the group consisting of benzene, naphthalene, anthracene, phen'anthrene, and homologues thereof under superatmosphcric pressure at a temperature between and 230 C. for a time limited to produce said phenolic compounds, in a reaction mixture containing sufflcient liquid hydrogen fluoride to minimize production of oxides of carbon and inflammable gases.

2. A process according to claim 1 in which phenol is formed by oxidizing benzene.

3. A-process according to claim 1 in which the oxidation is conducted in a reaction medium having as an oxygen carrier 2. compound of an element capable of changing its state of oxidation reversibly under oxidizing conditions.

4. A process according to claim 3 in which said oxygen carr er comprises silver as said element.

5. A process according to claim 3 in which said oxygen carrier comprises iron as said element.

6. A process according to claim 3 in which said oxygen carrier comprises copper as said element.

'7. A process according to claim 3 in which said oxygen carrier comprises arsenic as said element.

8. A process according to claim 3 in which said oxygen carrier comprises selenium as said element.

9. A process of oxidizing aromatic hydrocarbons selected from the group consisting of benzene, naphthalene, anthracene, phenanthrene, and homologues thereof to produce products comprising at least a major proportion of phenolic compounds and not more than minor proportions of carbon-containing products retaining the carbon ring structure of the reactant and containing no oxygen, which comprises oxidizing an aromatic hydrocarbon selected from the group consisting of benzene, naphthalene, anthracene, phenanthrene, and homologues thereof under superatmospheric pressure at a temperature between 0 and 200 C. in a reaction mixture con 75 2,367,731

taining liquid hydrogen fluoride for a time limited to produce said products, while maintaining the molecular ratio of the said aromatic hydrocarbon to liquid hydrogen fluoride not in excess of 3 to 1.

10. A process according to claim 9 in which the oxidation is conducted in a reaction medium having as an oxygen carrier a compound of an element capable of changing its state of oxidation reversibly under oxidizing conditions.

11. A process according to claim 9 in which phenol is formed by oxidizing benzene at a temperature between 50 and C.

12. A process according to claim 11 in which the oxidation is effected by an oxygen-containing gas at pressures between 500 and 1000 pounds per square inch.

13. A process of producing mono hydroxy nuclear substituted aromatic compounds which comprises oxidizing an aromatic hydrocarbon selected from the group consisting of benzene, naphthalene, anthracene, phenanthrene, and homologues thereof under superatmospheric pressure at a temperature between 0 and 200 C. in a reaction mixture containing liquid hydrogen fluoride and as an oxygen carrier a compound of an element capable of changing its state of oxidation reversibly under oxidizing conditions, maintaining the mole ratio of hydrocarbon to hydrogen fluoride not in excess of 3 to 1, and recovering the hydroxy aromatic compound thus formed.

14. A process according to claim 13 in which the oxidation is efiected by an oxygen-containing gas.

15. A process according to claim 13 in which the hydroxy aromatic compound is ortho-cresol and the aromatic hydrocarbon is toluene.

16. A process according to claim 13 in which the hydroxy aromatic compound is 2,4 dimethylphenol and the aromatic hydrocarbon is meta xylene. 17. A process of oxidizing benzene to phenol which comprises oxidizing the benzene under superatmospheric pressure at a temperature between 0 and 200 C. in a reaction medium containing liquid hydrogen fluoride, while maintaining the molecular ratio of the benzene to hydrogen fluoride not in excess of 3 to 1, said reaction medium having as an oxygen carrier a compound of an element capable of changing it state of oxidation reversibly under oxidizing conditions.

18. A process according to claim 17 in which the oxidation is efiected by gaseous oxygen.

19. A process of ox dizing benzene to phenol which comprises oxidizing the benzene under superatmospheric pressure at a temperature between 0 and 200 C. in a reaction mixture containing liquid hydrogen fluoride, while maintaining the molecular ratio of the benzene to liquid hydrogen fluoride within the range of 1:6 to 3:1, the reaction medium having as an oxygen carrier a compound of an element capable of changing its state of oxidation reversibly under oxidizing conditions.

20. A process according to claim 7 in which the oxidation is eifected by gaseous oxygen.

JOSEPH H. SIMONS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Moyer et al. Jan. 23, 19-15 Number Certificate of Correction Patent No. 2,530,369 I November 21, 1950 JOSEPH II. SIMONS It is hereby certified that error appears in the printed specification of the above numbered patent requlring correctlon as follows:

' Column 12, line 66, forthe claim reference numeral 7 read 19;

d and that the said- Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 1st day of May, A. D. 1951.

EHOMAS F. MURPHY,

Assistant Commissioner of Patents. 

1. A PROCESS OF OXIDIZING AROMATIC HYDROCARBONS SELECTED FROM THE GROUP CONSISTING OF BENZENE, NAPHTHALENE, ANTHRACENE, PHENANTHRENE, AND HOMOLOGUES THEREOF TO PRODUCE PHENOLIC COMPOUNDS WHICH COMPRISES OXIDIZING AN AROMATIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF BENZENE, NAPHTHALENE, ANTHRACENE, PHENANTHRENE, AND HOMOLOGUES THEREOF UNDER SUPERATMOSPHERIC PRESSURE AT A TEMPERATURE BETWEEN 0 AND 230*C. FOR A TIME LIMITED TO PRODUCE SAID PHENOLIC COMPOUNDS, IN A REACTION MIXTURE CONTAINING SUFFICIENT LIQUID HYDROGEN FLUORIDE TO MINIMIZE PRODUCTION OF OXIDES OF CARBON AND INFLAMMABLE GASES. 